Radwaste management | Packaging
A watchful guardian1 November 2012
A radio frequency identification (RFID) tracking system that was originally developed for the US Department of Energy can provide a wide range of information on the physical and radiological condition of waste drums. By J. Anderson, H. Lee, P. De Lurgio, C.M. Kearney, B. Craig, I.H. Soos, H. Tsai, Y. Liu, and J. Shuler.
Radio frequency identification (RFID) is a technology that can augment the existing safeguards and security measures at radiological facilities, and further enhance the protection of both materials and personnel [1-5]. Although commercial applications are already widespread, the use of this technology for managing nuclear materials is only in its infancy.
Since 2006, the Packaging Certification Program (PCP) in the US Department of Energy’s Office of Environmental Management (EM), Office of Packaging and Transportation (EM-63), has been working on an RFID system for nuclear materials management. The system, developed by Argonne National Laboratory, is known as ARG-US, derived from ‘argus’, which means a watchful guardian.
The system consists of tags, readers, and software for local and web-based applications. ARG-US utilizes sensors in the tags to continuously monitor the state of health of nuclear materials packaging and promptly disseminate alarms to authorized users [6-8]. In conjunction with GPS tracking, the system can also monitor and track packages during transport.
Argonne first tested key features of the RFID tracking system of nuclear materials packaging in a five-day, 1700-mile demonstration in 2008. Both the hardware and software platforms were verified to be stable and meet the performance requirements.
The DOE and national laboratories continued, meanwhile, to work several RFID system implementation projects at DOE sites, along with continuing device and system development .
Several ARG-US systems are in various stages of deployment and advanced testing at DOE sites, including the Nevada National Security Site, Sandia National Laboratory, Oak Ridge National Laboratory, Savannah River Site and Los Alamos National Laboratory.
Also, in July 2012, Argonne announced that it had finalized a licensing agreement with Evigia Systems that would see the system further developed and marketed to industry as a nuclear and hazardous material handling solution (see box). 
The tags for the ARG-US RFID system are battery-powered with built-in sensors for temperature, shock, humidity, seal, radiation (gamma), and battery strength. The front of the tag is covered by plastic to facilitate radio frequency transmission, and the back is sealed with a strong metal plate with a flange for attachment. Figure 1 shows the construction of an ARG-US tag. Because both the plastic cover and metal back plate are inexpensive and can be readily modified, the form factor of the ARG-US tags is versatile and can accommodate multiple types of packages, as shown in Figure 2.
For nuclear applications, the tag electronics must adequately resist radiation damage. In gamma-irradiation tests performed with a Cs-137 source, the tags were verified to function at a dose beyond 31 krad. This dose level corresponds to about 17 years of service in a field of 200 mR/h, the regulatory dose rate limit on the surfaces of Type B packaging. Since the actual surface dose rates are often significantly lower than the statutory limit, the lifespan of the tags would be proportionally longer.
The radio wave transceiver in ARG-US tags operates at 433 MHz and complies, for the most part, with the ISO 18000-7 standard . This frequency is globally accepted and widely used. Of particular significance is its suitability for use near metallic objects, such as metal drums or containers.
Other components on the tag’s motherboard include nonvolatile memory, a temperature sensor, a humidity sensor, a cantilever piezoelectric shock sensor, and the circuitry for processing the signals from a piezoresistive seal sensor (Figure 3).
The seal detector contains sensor elements that are pliant and force-sensitive; when they are compressed, their electric resistance drops, and when the load is removed, they bounce back and the resistance is restored. Monitoring the change in electric resistance gives a good indication on the seal bolt tension.
ARG-US nonvolatile memory can be programmed to store encrypted user data (for example, contents manifest), sensor data, and event histories. When the stored information is programmed, it may be used as the basis for an automated tickler system that addresses compliance with processing or maintenance requirements and schedules.
Low-self-drain, high-capacity lithium thionyl chloride (Li-SOCl2) primary cells are used in the tags. To further extend battery service life, a smart battery management board is incorporated (the right-hand compartment shown in Figure 1). Although up to four batteries may be loaded, auto-switching keeps only one battery on duty at any time. When the last battery is nearly depleted, an alert to call for replacement is automatically issued. Under normal usage, it is projected that this method provides up to ten years of service without requiring the battery to be changed.
To communicate with the tags via radio frequency, one or more interrogators (readers) are used. The communication is two-way: the readers can receive signals from the tags, and they can send instructions to them. The readers may be permanently mounted on a building structure or on mobile carts. The reading range can be greater than 100m, and no line-of-sight is required. Mobile handheld readers may also be used when the need arises.
Software provides the vital link between the technology and the end user, and is a key component in implementing ARG-US. The ARG-US software package consists of a program called ARG-US OnSite, local and central databases, and web applications for storage, processing, and transportation. ARG-US OnSite is the basic building block; it controls the readers via the control computer and provides a graphical user interface (GUI) to operate the hardware. The design philosophy is to present all relevant information on the console screen in a manner that can be intuitively understood by the user, so that by using pull-down menus, he or she can efficiently obtain information and issue commands (Figure 4). Within a secure internet space, information from multiple rooms, buildings, or sites can be linked together by using the ARG-US web applications. The information can be accessed by authorized users located anywhere at any time. ARG-US TransPort (a subset of the ARG-US system) can monitor and track nuclear or radioactive materials in transport. It incorporates mapping and a global positioning system (GPS) and uses mobile communication equipment in the transport vehicle (Figure 5).
Adding a dosimeter
To further extend the functionality of the ARG-US RFID system, a gamma dosimeter has been incorporated into the tags to augment the existing sensors (temperature, humidity, seal, shock, and battery strength). The dosimeter regularly samples the dose rate and accumulates a total dose estimate that is stored in nonvolatile memory. The frequency is user-adjustable. In a static storage situation, the frequency may be several times a day. In more demanding situations, the interval between sampling could be measured in minutes.
In facilities with a large number of packages, dose rate readings from the tags can be collected to precisely map the radiation field; any significant perturbation from the norm can be used to generate alarms, thereby enhancing the safety, security, and safeguards of the operation. Because the radiation field data are constantly available, the number of routine manned inspections with handheld detectors (particularly those over local areas with high radioactivity) may be curtailed, thus reducing the exposure of personnel to radiation. The dosimeter expansion via a carrier board is designed to facilitate the future development and integration of other types of sensors beyond gamma dosimeters.
The gamma detector modules selected for incorporation into the ARG-US tags are modified compact personal dosimeters available off the shelf. The principal features considered in selecting them were their size, power consumption, operating dose-rate range, reliability, and cost.
The selected detector is sensitive to X-ray and gamma radiation in an energy range of 50 keV to 6 MeV and has a wide dynamic measurement range—from 0.1 mSv/h to 8 Sv/h. A carrier board is used to mount the detector module and facilitate the tag integration (shown on the left in Figure 1). The module carrier board is easily detachable should dosimetry be unnecessary for an application.
The data from the dosimeter are collected by a low-power micro-controller unit (MCU) on the carrier board. The nonvolatile memory implemented within the MCU allows the accumulated dose rate information to be retained when the power is off. Careful power management and a judicious selection of components resulted in the impact of the dosimeter on battery performance being only minor. In the low-power mode of the carrier board, the MCU is set, at regular programmeable intervals, to ‘wake up’ the dosimeter and read the instantaneous dose rate. The data are passed along through the tag to the reader network whenever those values are requested. The requested data are then displayed at the operator terminal and stored in the system database. Data on alarm events that have resulted from high or low dose rates or a high accumulated dose are stored in both the MCU and the database. To allow the tags to be used in discrete processing or shipping campaigns, the cumulative dose can be reset by the user via the radio frequency link and ARG-US interface. Figure 6 shows a simplified block diagram of the dosimeter integration in the tag structure.
The communications protocol between the carrier MCU and the ARG-US RFID tag, and the RFID tag firmware design, are designed to be independent of the number and type of sensors attached to the carrier board. This flexible interface allows the MCU of the carrier board to simply identify the amount of data present. In addition to its data processing, tag interface, alarm initiation, and power management features, the custom-built carrier board has provisions to accept additional sensors, including external ones, through its versatile mix of interfaces. The additional sensors being considered include speciality gas sensors, enhanced seal and tamper indicators, and neutron detectors.
Benchmark testing (Figure 7) with a certified Cs-137 source was performed for the lead tags to verify that the integrated dosimeters were functional. The testing was performed at six dose rates (10, 50, 100, 150, 200 and 1000 mR/h), with the longest exposure being 24 hours. The reported dose rates are from the most up-to-date, facility-published exposure rate table traceable to the National Institute of Standards and Technology standard.
All benchmark testing results were in good agreement with the published data on dose rates, which indicates that the selected dosimeters are accurate. An equally important result is the ability to read off the dosimeter output via radio frequency, which indicates that the tag integration effort was successful.
Figure 8 shows the two tested tags yielding a steady reading over a period of 24 hours at a constant dose rate of 100 mR/h. The integration of the dose rate into the cumulative dose was also accurate.
By changing the distance between the tags and the source and by using proper attenuators, the dose rates were varied to determine the dosimeter performance over a range of anticipated field conditions. These results are shown in Figure 9. Again, the behaviour of the integrated dosimeters was highly satisfactory. Note that in both cases the self-shielding of the front plastic case of the tags accounted for the ˜4% reduced readings of both the dose rates and cumulative doses.
On the basis of these positive findings, the selection of the dosimeter and the design of the carrier board were finalized, and the production of the first batch of dosimeter-enabled ARG-US RFID tags was launched.
A test of the ARG-US RFID gamma dosimetry sensor in a true radioactive material storage environment was recently carried out at the Savannah River Site’s (SRS) K Facility (an active Category I Plutonium Storage Facility). Twelve ARG-US RFID units, with built in gamma dosimeters, were placed into the 910-B Storage Vault in February 2012. This vault experiences high traffic of type B shipping packages containing radioactive material during facility operation. The field test was due to run for six months, also aimed to assess the sensor functionality and battery strength of the unit.
This article was published in the October 2012 issue of Nuclear Engineering International
J. Anderson, H. Lee, P. De Lurgio, C.M. Kearney, B. Craig, I.H. Soos, H. Tsai and Y. Liu, Argonne National Laboratory, Argonne, IL 60439.
J. Shuler: U.S. Department of Energy, Washington, D.C. 20585
This article is based on paper 12009 “Tracking and Monitoring with Dosimeter-Enabled ARG-US RFID System”, presented at the WM2012 conference February 16 – 1 March in Phoenix, Arizona.
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10. Argonne, Evigia finalize licensing agreement for next-gen RFID sensor technology, 16 July 2012.
11. SMBus (System Management Bus), specifications, home page, http://smbus.org.
|Future development with commercial partner Evigia|
Several years of cooperative development work between ANL and Evigia culminated in a licensing agreement concluded in July 2012. The agreement will allow Evigia to take the second-generation EV-3 e-seal technology (jointly developed by Evigia and ANL engineers) and the ARG-US software (developed by ANL) to market for nuclear and other hazardous material storage/transport applications. Since the ARG-US system has been deployed by ANL at several test sites, and has already been through a couple of iterations of updates based upon those initial users, it is ready for commercial applications. Likewise, the EV-3 RFID sensors have been tested extensively both in lab and real-world use, Evigia says.